HF Magnetic Loop for Chasing SOTA – Part 1

Magnetic Loop Antenna for SOTA chasing 12 October 2013

During the week I made a home-brew HF Magnetic Loop antenna for chasing SOTA activators.  Today I get to try it out!

The main loop is 3/8 inch copper pipe 1 metre in diameter and mounted 1.5 metres above the ground.  The inner loop (temporary) is 2 mm copper wire formed to make a 200 mm diameter loop.  The inner loop will be replaced with a copper pipe loop of the same diameter, it’s now ready to mount.  The tuning range of the loop is 7 MHz to 22 MHz.

The tuning capacitor is an E.F. Johnson dual gang 200 pf per section.  Additional capacitance is required to tune 40m, I have used a 63 pf doorknob capacitor to switch across the main tuning capacitor.  Tuning is very narrow with the standard tuning knob.  I have a 5:1 vernier dial and a shaft insulator to add to the capacitor rotor, but for now is works well.

Today I chased 3 SOTA stations using a Yaesu FT-817, 5 watts output into the Magnetic Loop antenna.  Signal reports were:

Josh VK2JOS on VK2/HU-054, report 5-7 and 5-6
Andrew VK2FAJG on VK2/ST-001, report 5-6 and 3-4
Glenn VK3YY on VK3/VT-022 5-5 and 5-5
Glenn VK3YY on VK3/VT-013, 5-4 and 5-5
Glenn VK3YY on VK3/VT-016, 5-5 and 5-2
I could hear Mark VK3PI, just wasn’t quick enough to call him, I was busy making a 40m/20m link dipole for the VK1 loan SOTA kit.

I could not hear Ed VK2JI on Mount Elliot.

Fig 1:

Magnetic Loop Antenna 1 metre diametre

Fig 1: Magnetic Loop Antenna 1 metre diameter

Fig 2:

Inner Loop 200 mm diametre

Fig 2: Inner loop 200 mm diameter

Fig 3:

Heavy braid to reduce losses

Fig 3: RG213 braid used to reduce losses

Fig 4:

Tuning Capacitor

Fig 4: E.F Johnson 200 pf dual section tuning capacitor

Fig 5:

80 pf door knob capacitor

Fig 5: 80 pf doorknob capacitor connected in circuit with a large clip

Very happy with the home-brew Magnetic Loop and the noise reduction.

For later updates see:

HF Magnetic Loop for Chasing SOTA – Part 2

HF Magnetic Loop for Chasing SOTA – Part 3

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4 thoughts on “HF Magnetic Loop for Chasing SOTA – Part 1

  1. Pingback: HF Magnetic Loop for Chasing SOTA – Part 3 | VK1NAM Summits on the Air (SOTA)

  2. Pingback: HF Magnetic Loop for Chasing SOTA – Part 2 | VK1NAM Summits on the Air

  3. Obviously it’s more broadband than a dipole on 40 metres but how does it compare performance wise within band? Or was that the antenna test on the weekend? 🙂

    • Hi Andrew, the loop wasn’t a part of the antenna tests on Sunday, it’s too big and bulky to carry 4 km to a summit. I could take it to a local summit with vehicle access, something to think about.

      While I didn’t check the actual performance of the mag loop against the 40m dipole at 8 metres, I would take a stab and say signal reports were 2 to 3 S points lower using the loop. For example Glenn VY3YY is often 5-8 at my QTH on the dipole. On Saturday he was consistently 5-5 via the mag loop. The mag loop is only 1.5 metres above ground level.

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